Diene Termonomer Type and EPDM Properties

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Abstract
The objective of this work was to study the effects of the type of diene termonomer on properties, especially thermal stability and aging, of EPDM polymers. Five different EPDM polymers using ethylidene norbornene (ENB), butadiene (BD), dicyclopentadiene (DCPD), methyltetrahydroindene (MTHI), and 1,4-hexadiene (HD) as termonomers were made at equimolar unsaturation. The same sulfur/accelerator system was used for curing these polymers. In both gum and filled vulcanizates ENB-EPDM is the fastest curing. In gum stocks HD-EPDM is the slowest curing, but is faster than DCPD-EPDM in filled stocks. These polymers, except for BD-EPDM, have about the same initial crosslink densities. Crosslink density and crosslink type analyses indicate that butadiene units in BD-EPDM chains are blocked. For HD-EPDM, both in gum and filled vulcanizates, 50 per cent of original crosslinks are monosulfidic. The other four EPDM vulcanizates have a lower proportion of monosulfidic crosslinks. At 350° F aging temperature, both ENB and HD polymers have ∼65 per cent monosulfidic crosslinks and about the same energy-to-break values (Eb). However, the higher original monosulfidic crosslink content of HD-EPDM does not seem to offer any better aging than for other polymers. DCPD-EPDM at 350° F aging temperature has the same monosulfidic content but increases further at 550° F aging temperature. At 550° F aging temperature almost all the crosslinks are monosulfidic for these EPDM polymers but the total crosslink densities and Eb are very low presumably due to oxidative degradation. Thermogravimetric analysis in N2 shows that these vulcanizates decompose in 800-935° F temperature range. In air, this range is 750-935° F.

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